Vinyl chloride resins are widely used for molding materials and the like based on their characteristics, but have various processing problems such that the thermal decomposition temperature is close to a processing temperature, therefore the processing condition is limited, and fluidity is poor. However, it is known that blending a high-molecular-weight (meth)acrylic polymer powder having methyl methacrylate as a principal component promotes gelling of a vinyl chloride resin in molding process, and improves the appearance of a molded product, leading to application to vacuum molding and profile extrusion molding.
In contrast, foaming is one of the methods of molding a vinyl chloride resin, and an attempt of adopting this molding method is made to reduce the weight of the vinyl chloride resin and use the product as a wood substitute material. However, in the case that a high-molecular-weight (meth)acrylic polymer powder is added to a vinyl chloride resin to produce a foam molded product, the production is problematic in that the melt elongation and melt strength of the vinyl chloride resin are insufficient, and therefore a foam molded product insufficiently foams and foaming cells are ununiform. In addition, the vinyl chloride resin has a limited molding condition. Therefore, it is difficult to produce a foam molded product having excellent appearance and a sufficient expansion ratio only by changing the processing conditions.
In order to overcome these disadvantages, various methods have been proposed for providing a vinyl chloride resin having a sufficient expansion ratio without impairing the appearance. The methods comprise blending a (meth)acrylic polymer powder having an ultrahigh-molecular-weight methyl methacrylate as a principal component so as to impart good melt strength (see, for example, Patent Documents 1 to 3). These methods provide a vinyl chloride foam molded product having a high expansion ratio without impairing the appearance of a foam molded product.
However, when such an ultrahigh-molecular-weight (meth)acrylic polymer powder is added to a vinyl chloride resin, a (meth)acrylic polymer is insufficiently dispersed in a vinyl chloride resin, problematically leading to insufficient improvement in melt strength. In addition, a large cell size and contraction of a foam molded product occur, and they problematically result in poor appearance of the foam molded product.
Patent Document 1: JP-B 3892225
Patent Document 2: JP-A 2005-255717
Patent Document 3: JP-A 2006-282901